Make EbpfError enum discriminant size explicit

src/error.rs

@@ -24,6 +24,7 @@ pub trait UserDefinedError: 'static + std::error::Error {}
 
 /// Error definitions
 #[derive(Debug, thiserror::Error, PartialEq, Eq)]
+#[repr(u64)] // discriminant size, used in emit_exception_kind in JIT
 pub enum EbpfError<E: UserDefinedError> {
     /// User defined error
     #[error("{0}")]

tests/ubpf_execution.rs

@@ -4158,6 +4158,51 @@ fn test_tcp_sack_nomatch() {
     );
 }
 
+#[inline(never)]
+fn copy_ebpf_error(err: &mut EbpfError<UserError>) {
+    *err = EbpfError::DivideByZero(0);
+}
+
+#[inline(never)]
+fn copy_result(err: &mut Result) {
+    *err = Result::Err(EbpfError::DivideByZero(0));
+}
+
+#[test]
+fn test_result_discriminant_size() {
+    unsafe {
+        // Create a Result<u64, EbpfError<UserError>> filled with 0xaa
+        let test: [u8; std::mem::size_of::<Result>()] = [0xaa; std::mem::size_of::<Result>()];
+        let mut test_result =
+            std::mem::transmute::<[u8; std::mem::size_of::<Result>()], Result>(test);
+        // Overwrite the Result with another result
+        copy_result(&mut test_result);
+
+        // Check that all 64-bits of the discriminant were changed
+        let err_kind = *(&test_result as *const _ as *const u64);
+        assert_eq!(err_kind, 1u64);
+    }
+}
+
+#[test]
+fn test_err_discriminant_size() {
+    unsafe {
+        // Create a EbpfError filled with 0xaa
+        let test: [u8; std::mem::size_of::<EbpfError<UserError>>()] =
+            [0xaa; std::mem::size_of::<EbpfError<UserError>>()];
+        let mut test_err = std::mem::transmute::<
+            [u8; std::mem::size_of::<EbpfError<UserError>>()],
+            EbpfError<UserError>,
+        >(test);
+        // Overwrite the EbpfError with another error
+        copy_ebpf_error(&mut test_err);
+
+        // Check that all 64-bits of the discriminant were changed
+        let err_kind = *(&test_err as *const _ as *const u64);
+        assert_eq!(err_kind, 7u64);
+    }
+}
+
 // Fuzzy
 
 #[cfg(all(not(windows), target_arch = "x86_64"))]